Motor vehicles and automotive parts in particular are today provided with base coat/clear coat two-layer coatings, predominantly with a corresponding special effect coating comprising a base coat which imparts color and/or lightness flop (special effect-imparting base coat, special effect base coat) and a protective, gloss-imparting clear coat applied thereover. “Color and/or lightness flop” describes the behavior of such coatings with regard to imparting a different apparent color and/or lightness when observed from different angles. This behavior is obtained as a consequence of special effect agents or pigments contained in the special effect base coats, in particular, for example, metal flake pigments or mica pigments.
When producing single-tone base coat/clear coat two-layer coatings, the single-tone base coat is conventionally applied by means of electrostatically-assisted high-speed rotary application. This is not conventional when producing special effect base coat/clear coat two-layer coatings, the special effect base coat instead generally being applied in two spray passes. In this case, spray application proceeds in the first pass by means of electrostatically-assisted high-speed rotary application (approximately 60–70% of the special effect base coat layer), while, in the second pass, spray application generally proceeds by pneumatic spraying without electrostatic assistance (approximately 30–40% of the special effect base coat layer), c.f. A. Goldschmidt and H.-J. Streitberger, BASF-Handbuch Lackiertechnik [BASF coating techniques handbook], Vincentz Verlag, Hanover, 2002, page 730. While the final pneumatic spray application does indeed have the disadvantage of lower application efficiency associated with increased losses due to overspray, it guarantees excellent optical quality of the finished special effect base coat/clear coat two-layer coatings with regard to pronounced and uniform development of the special effect, avoidance of clouding and overall appearance. If the subsequent pneumatic spray application is replaced by electrostatically assisted high-speed rotary application, the optical results achieved are generally less good, in particular, in the case of special effect base coats in very light metallic shades or with a strong color flop.